Dielectric materials



S ATENT OFFICE 2,174,512 DIELECTRIC MATERIALS lLee Cone Holt, lEdgemoor, and Herbert Wilkens 'Daudt, Wilmington, DeL, assignors to Kinetic Chemicals, Inc., Wilmington, DeL, a corporation of Delaware No Drawing. Application November 24, 1933,

\ Serial No. 699,636

21 Claims. (01. zsz-lj This invention relates to dielectric materials. Table A I more particularly liquids having dielectric properties and the application thereof '1 etrachlorobenzo- The use of liquids is required in certain electri- Bemomfluonde trifluoride cal equipment, such as, for example, transform- 5 ers, capacitors, condensers and switch boxes. gf g gf 1 gg-g i i- Among the functions of the liquid are those of v z is 'ijff jj 2 'jjjjj 35 removing heat and of allowing the making of cong (at tact in the absence-oi air or of explosive mix- Dielectri c0nstant,(at100 4.1. ures. The requiremen s for such liquids are, 10

R 1.4 9 4 1 among other things, very high resistance to the c X10 0 flow of electric currents, high stability to atmosg$f Infiammame flg 1min pheric conditions at ordinary and at somewhat flmnmagle. elevated temperatures, high resistance to thermal igm in organic Miscible Miscib1el5 decomposition, low vapor pressure, low congealing pecqmbosition a boiling N11, 5

temperature, low inflammability and high flash g ggg action on Steel Nil point. Preferably, the liquids should be mobile Corrosive action on copper: even at relatively low temperatures and should be Action on N Actlon on Bakelite N11. good heat transfer agents. In commercial raotise, high-boiling fractions m p Tetrachlorobenzotrifluoride may be prepared by of petroleum distillates have been largely used for this purpose. These liquids do not satisfy all of the above stated requirements. They are relatively poor heat transfer agents and, under the conditions of their use, they gradually decompose with the formation of undesirable products which adversely influence the electrical properties. Some of these products are tarry; others are appreciably volatile and may present fire and explosion hazards.

It is an object of the present invention to provide new and improved dielectric media. A further object is the provision of liquids which are applicable in insulating electrical conductors in electrical equipment such as, for example, transformers, capacitors, condensers and switch boxes. other objects will appear h i ft and the water-insoluble material extracted with In accomplishing these objects according to dilute aqueous hydrochloric acid. Subsequently, this invention, it has been found that alp it was washed w1th water and d1lute sodium by- 4 compounds containing fluorine in the Side chain! droxide solution. Theseparation of the product preferably alphyl compounds in hi h ,11 of the was assisted by extraction with ether. This prodhydrogens of the side chains have been substi- 11613 was diFSOIVed in ethe? and the 59111131011 agfim tuted by fl in possess good dielectric proper washed w1th dilute sodium hydroxide solution. ties and are suitable for application as dielectric The extfacted ether solutlon was dehydrated media. Compounds such as benzotrifiuoride are "after Q the solvenfl was QVaPOraFBd- 45 r ferred to such compounds as benzyl and benza1 The residue was subJected to fractional d1st1llafluorides, benzofiuorodichloride and benzodifiuotion- A number of fractlons of Various Chlorirochloride because of greater stability. The same Rated Products were Obtainedone Of these fraccomparison holds between derivatives of benzolJiOIlS boiled Within the range s trifluoride and the corresponding derivatives of chlorine content as a d it co s ted 5- 50 the other compounds just noted. sentially of tetrachlorobenzotrifluoride (theoreti- The following table illustrates the properties of cal chlorine content 50.0%). This product was two of the substances falling within the scope of fu r p fie P o t0 making e tests d the invention, viz., benzotrifiuoride and tetrascribed above.

ehlorobenzotrifluoride. In general, chlorinated benzotrifiuoride comthe chlorination of benzotrifluoride. The chlorination may be effected according to well known methods for the chlorination of aromatic compounds. For example, tetrachlorobenzotrifiuoride 25 was produced as follows:

Four hundred fifty (450) parts of benzotrifluoride, 2 parts of anhydrous ferric chloride and 20 parts of iron borings were placed in a glass flask and chlorine gas added to the reaction mass dur- 30 ing a period of twelve hours. During this period the temperature was gradually increased from 20 C. to C., and the reaction was continued until an increase in weight of 318 parts was obtained. 35

The cooled reaction mass was drowned in water pounds containing chlorine in the aromatic ring can be prepared by the general method above described, which is a known method for chlorinating aromatic compounds although, insofar as we are aware, it'has never been appliedin the preparation of chlorobenzotrifluorides. Chlorinated benzotrifluoride mixtures obtainable by the chlorination of benzotrifluoride possess the desired properties. A chlorinated mixture of benzotrifluoride having a chlorine content of 44.05% boils. at 201 C. to 240 C., freezes at --41 C., and has a specific gravity of 1.629. The low congealing temperature of this mixture makes it especially desirable for low temperature uses.

One or more of the ring hydrogen atoms of the alphyl compound may be replaced by other sub-' stituent groups or atoms so long as they do not adversely influence to an undesirable degree the essential electrical and physical properties and the stability. In general, the preferred compounds are non-acidic and are free from groups which readily hydrolyze to form acidic groups. Among the substitution'products that might be utilized, there may be mentioned those in which one or more ring hydrogen atoms of a fluorinated alphyl hydrocarbon containing fluorine in the side chain has been substituted by groups or atoms such as Cl, --Br, NH2, F, CF3, NO2, aryl, alkyl, aralkyl, alkylamino and dialkylamino, more specifically compounds such as, for example, trifluoromethylbenzenes, trifluoromethylchlorobenzenes, fluorodibenzyls containing fluorine in the side chain, trifluoromethylfiuorobenzenes, di-(trifiuoromethyl) -benzenes, and similar fluorinated derivatives. It will be understood that the results with all compounds are not comparable and that better results are obtained with some compounds than with others, since their properties may vary widely as to boiling point, inflammability, etc. Benzotrifluoride has the combined advantages of high electrical resistance, high stability, liquidity at low temperatures, and low viscosity. Halogenated derivatives such as chlorinated benzotrifluorides have the additional advantages of low inflammability and low vapor pressure.

The boiling point of some of the compounds falling within the invention are given by the following table:

Table B Compound Boiling range o I Benzotrifluoridc 102-1025. o-Chlorobcnzotrifiuoride 151-153.

m-Brom-benzotrilluoride 156-157. m-Arninobcnzotrifluoride 188-189. m-Dimethylaminobenzotrii'luoride 202.5-203 3 m-Dieth ylaminobenzotrifluoride 212-215 m-Iodobcnzotriiluori lc 182-183 Bromo-m-dimcthylaminobenzotrifluoridc Z-chlorod :Bdi (triliuoromcthyl)-bcnzcnc 155-160 '2-chloro-4nitrobenzotrifluoridc 102403) (AL 5 mm. 2 chloro-4-aminobenzotriiluoridc -103 ()At 6 to 7 mm. 2-methoxy-i-aminobenzotril'luoride 248449.

to decomposition by the usual whereas the CC1: group,

able application of this inventionis the use of benzotrifluoride and/or its substituted derivatives in mixtures with other materials that are less inflammable and have lower vapor pressures, e. g., chlorinated benzotrifluorides.

The present invention provides substances which are eminently suitable for use as dielectric materials. While the characteristics of these substances may vary, they have, in general, the requirements of dielectric materials. In 'particular, it should be noted that the CF; group, which characterizes benzotrifluoride and its derivatives, is exceedingly stable and is not subject hydrolytic agents, which characterizes benzotrichloricle and its derivatives, is very unstable, being readily hydrolyzed to the carboxylic acid group.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that we do not limit ourselves to the specific embodiments thereof except as defined in the following claims.

We claim:

1. A dielectric medium comprising, in liquid phase, a chlorobenzotrifluoride in which the chlorine is substituted in the aromatic ring and which boils above 200 C.

2. Tetrachlorobenzotrifluoride, a boiling at approximately 247 C. to 249 a freezing point at about 10 about 35 seconds at 37.8 stant at 25 C. of about 4.5, said compound being useful as such or in admixture with other dielectric substances as a dielectric medium.

3. The process which includes insulating eleccompound C., having trically conducting materials by separating themwith a medium comprising substantial propor trically conducting materials by separating them with a medium comprising substantial proportions of a mixture of chlorinated benzotrifluorides.

5. The process which includes insulating electrically conducting materials by separating them with a medium comprising essentially a mixture or the chlorinated derivatives of benzotrifluoride including tetrachlorobenzotrifluoride.

6. The process which includes insulating electrically conducting materials by separating them with a medium comprising essentially a mixture of the chlorinated derivatives of benzotrifiuoride including a polychlorinatedbenzotrifiuoride which boils above 200? C.

'7. The process which includes insulating electrically conducting materials by separating them with a medium comprising substantial proportions of a mixture of chlorinated benzotrifluorides with benzotrifiuoride.

8. The process which includes insulating electrically conducting materials by separating them with a medium comprising substantial proportions of a non-acidic benzotrifluoride.

9. The process which includes insulating electrically conducting materials by separating them with a medium comprising substantial proportions of benzotrifluoride.

C., a-viscosity of C., and a dielectric con- 10. An electrical device containing a dielectric material comprising substantial proportions of a liquid alphyl compound containing fluorine in the side chain.

11. An electrical device containing a dielectric material comprising substantial proportions of benzotrifiuoride.

12. A dielectric medium comprising a liquid mixture of a substantial proportion of a fluorinated alphyl hydrocarbon containing fluorine in the side chain and a substantial proportion of a substance compatible therewith selected from the group consisting of hydrocarbons and their ch10- rinated derivatives that are stable to atmospheric conditions and have a relatively high boiling range.

13. A dielectric medium comprising a liquid mixture of a substantial proportion of a noninflammable fiuorinated alphyl hydrocarbon containing fluorine in the side chain and a sub-- stantial proportion of a substance compatible therewith selected from the group consisting of hydrocarbons and their chlorinated derivatives that are stable to atmospheric conditions and have a relatively high boiling range.

14. A dielectric medium comprising a liquid mixture of a substantial proportion of benzotrifluoride and a substantial proportion of a ring halogenated cyclic hydrocarbon which is miscible therewith, stable to atmospheric conditions and boils above 200 C.

15. A chlorobenzotrifluoride which is stable to atmospheric conditions and boils above 200 C.

16. A mixture of benzotrifiuorides containing a normally liquid chlorobenzotrifiuoride which is stable to atmospheric conditions and boils above 200 C.

17. Mixtures of poly-chloro-benzo-tri-fluorides stable to atmospheric conditions and boiling above 200 C.

18. An electrical device containing a dielectric material comprising substantial proportions of a trifiuoromethyl-fiuoro-benzene.

19. A dielectric medium comprising'a liquid mixture of .a substantial proportion of a trifiuoromethyl-fluoro-benzene and a substantial pro-. portion of a substance compatible therewith selected from the group consisting of hydrocarbons and their chlorinated derivatives that are stable to atmospheric conditions and have a relatively high boiling range.

20. The process which includes insulating electrical conducting materials by separating them with a medium comprising substantial proportions of a trifluoromethyl-fluoro-benzene.

21. A dielectric medium comprising in liquid phase a trifiuoromethyl-fluorobenzene in which fluorine is substituted in the aromatic ring.

LEE CONE HOLT. HERBERT WILKENS DAUDT. 

